U.S. Pat. No. 4,719,761 to Cromer, the same inventor as the subject invention, encompassed a cooling system. The Cromer '761 patent was a method and apparatus for increasing removal of moisture in a cooling system which provided for a desiccant to contact and evaporate moisture into dry feed air prior to passing the feed air over cooling coils in order to increase the dew point (moisture content) of the feed air. This increases the moisture removal of the cooling system. The desiccant material is loaded with moisture by absorption of moisture from the moisture saturated air leaving the cooling coils. The method included removing the moisture by a desiccant from the saturated air leaving a cooling means and delivering it to air entering the cooling means which significantly increases the dehumidification of the air passing through the cooling means. The cycling of moisture from the saturated air leaving the cooling coils and evaporating this same moisture into the air entering the cooling coils for the enhanced dehumidification of the coils has become known as the "Cromer Cycle" and is the subject of prior U.S. Pat. No. 4,179,761 by the subject inventor thereof, which is incorporated by reference.
Attempts have been proposed to use desiccants. See for example, U.S. Pat. No. 3,766,660 to Settlemyer and U.S. Pat. No. 4,125,946 to Prager. However, these patents use an external heat source to dry the desiccant which is energy inefficient. U.S. Pat. No. 5,092,135 to Cameron uses a vacuum to dry the desiccant, a very energy inefficient process. The U.S. Pat. No. 4,057,907 to Rapino, et al. uses the combination of several drying methods: a vacuum, microwaves, ultrasonics and cosolvents, on the material to be dried to increase the drying rate, but these methods are also very inefficient in the BTU moisture removed per BTU energy expended. Materials are typically dried by passing heated air over the material. In these systems, they start by converting only 50% of the energy input into moisture removal. At the end of the drying process, typically only 10% of the energy input is converted into moisture removal. There heated-air systems average no better than 30% of the input energy into removal of moisture. Attempts have been made to improve efficiencies by recouping some of the heat by heat exchangers or heat pipes as in the U.S. Pat. No. 5,343,632 to Dinh.
The vapor compression cooling system moves heat more efficiently than it can be created by burning fuel. It may be applied to a closed loop dryer system as in U.S. Pat. No. 3,922,798 to McMillan. However, only slight improvements in efficiencies are obtained over heated air systems because the cooling coil typically removes only 20-25% of its work in moisture, the remaining 80% goes to cool the air which must be reheated by the condenser. U.S. Pat. No. 5,343,632 to Dinh attempts to reduce the amount of reheat needed by recouping some of the heat by heat exchanger or heat pipes.
The use of a desiccant to transfer moisture from the air leaving the cooling coil to the air entering the cooling coil not only increases the dryer temperature and reduces the dryer air humidity which increases the air capacity to remove moisture from the product, it also improves the moisture removal of the cooling coil as much as 70% of the work going to moisture removal and only 30% going to cool the air. This provides substantial energy efficiency improvement over previous drying methods in the conversion of energy input to moisture removal.